The invention relates generally to an assembly and a method for positioning a retaining ring and more particularly to an assembly and method for positioning a rotor retaining ring using a hydraulic mechanism.
Assembly of an electric machine often includes assembling a rotor that is provided with a radially compressive pre-stress by installing a pre-fabricated retaining ring with an interference fit over the rotor. The pre-stress of the rotor is used to contain centrifugal forces during high speed rotation. In order to achieve the pre-stress of the rotor, a cross-sectional inner diameter of the retaining ring is made smaller than an outer diameter of the rotor, and the retaining is expanded to achieve an interference fit over the rotor. The traditional process used to expand a retaining ring is the application of heat to cause thermal expansion. However, if the retaining ring is fabricated using a material that does not expand significantly or in desired amount and direction when subjected to temperature changes, or does not have adequately high temperature limits, then this may result in insufficient pre-stress of the rotor after the installation of the retaining ring. Materials ideally suited for use in many rotating assemblies, such as fiber reinforced composites, are known to have limited maximum acceptable temperatures and limited rates of thermal expansion. These materials therefore do not lend themselves to assembly by thermal expansion.
A second problem encountered in the use of thermal shrink fitting procedures is due to non-uniform expansion. A warped rotor can occur if the retaining ring expands in a manner that is not uniform because the temperatures everywhere in the part are not the same, or because the material thermal expansion characteristics everywhere in the part are not the same.
Accordingly, there is an ongoing need for efficient assembly and disassembly of a retaining ring with negligible frictional resistance and optimal use of high specific strength materials.